<nav class="navbar navbar-expand-lg navbar-light bg-light fixed-top">
  <div class="container">
    <a class="navbar-brand" href="#">在线竞拍</a>
    <!--用于网页缩小后，导航栏缩放 data-target="#navbarNavDropdown" 对应需要缩放的div框-->
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavDropdown"
            aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
      <!--一根横线-->
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarNavDropdown">
      <ul class="nav navbar-nav">
        <li class="nav-item active">
          <a class="nav-link" href="#">关于我们 <span class="sr-only">(current)</span></a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">联系我们</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">网站地图</a>
        </li>
        <li class="nav-item dropdown">
          <a class="nav-link dropdown-toggle" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true"
             aria-expanded="false">
            详细信息
          </a>
          <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
            <a class="dropdown-item" href="#">关于我们</a>
            <a class="dropdown-item" href="#">联系我们</a>
            <a class="dropdown-item" href="#">网站地图</a>
          </div>
        </li>
      </ul>
    </div>
  </div>
</nav>
